The partial wave unitarity bound for the elastic \(2\rightarrow 2\)  scattering processes in the high energy limit restricts scalar couplings in the Higgs potential.
In Ref. [1]}, the unitarity bounds were applied to the SM
to derive an upper limit on the mass of the Higgs boson.
A similar argument can be made for the extended Higgs models.
In Ref. [2]}, the tree-level unitarity bounds were derived in the framework of 3HDM with \(Z_{3}\)  symmetry.
Following the results of Ref. [2]},
we can obtain eigenvalues \(\Lambda _{i}\)  (\(i=1-21\) ) for the partial waves of the \(S\) -matrix amplitudes for \(2\rightarrow 2\)  scattering processes with the replacement
\(r_{1-3}=\lambda _{1-3},\ r_{4-9}=\frac{1}{2}\lambda _{4-9},\ c_{11}=\frac{1}{2}\lambda _{10}\; ,\) 
